Basic studies of the synthesis and degradation of extracellular matrix are concentrated on evaluation of collagen production by human fibroblasts. These cells regulate collagen production by altering collagen mRNA levels and by destroying newly synthesized collagen within the cell prior to secretion. Genes have been isolated for sheep and human collagen pro alpha2 chains. Alveolar macrophages and the eosinophils have been evaluated for their role in the destruction of the connective tissue matrix. While the alveolar macrophage produces collagenase and elastase, this production is constitutive and likely play little role in the pathogenesis of disease. However, the eosinophil can produce collagenase in significant quantities. Mesothelial cells have been evaluated in culture and have been shown to produce many types of connective tissue components including collagen types I, III, and IV, elastin, fibronectin and laminin.